André Villas-Boas arrived on a £13m "transfer" from Porto cocksure from a Europa League, Portuguese Cup and championship treble and intent on tearing up an ageing Chelsea team. Roman Abramovich had paid that compensation fee because the Chelsea owner saw a young vibrant manager who could take on John Terry, Frank Lampard, Didier Drogba and company.

Now, humbled by Stamford Bridge's internecine rumblings and the sheer weight of the senior players' influence, the 34-year-old takes Chelsea to Napoli for a last-16 Champions League first leg unsure just how much longer he will have to complete the job: lose like Arsenal did when going down 4-0 at Milan last week and Villas-Boas' chances of taking charge of the return leg will hardly be enhanced.

This 1-1 draw against an impressive Birmingham City was a Saturday afternoon sleepwalk for a side that missed Terry, who is injured, Drogba and Lampard, the latter pair coming on during the FA Cup tie. Chris Hughton's team deserve praise for an accomplished performance but at a venue once a fortress under José Mourinho, they should never have been allowed to play their game.

In three breathless first-half minutes David Murphy was allowed to blast home from a corner that bounced twice across the Chelsea area, then Juan Mata's penalty was saved superbly by Colin Doyle. On came Drogba at the interval for Fernando Torres, who is enduring a personal nightmare, and Chelsea roused themselves enough to force a replay, Daniel Sturridge's slick header just after the hour ensuring Chelsea may yet progress to the sixth round, where they would face Leicester City at home.

Villas-Boas said of a group of players who have lost their way and confidence: "That comes with results, we are pushing very hard to get it. We played very well in the second half and showed a good response to adversity again. We didn't create enough opportunities to win."

Napoli defeated Manchester City 2-1 in a Champions League group game in November, both goals scored by the Uruguay striker Edinson Cavani, and ended a five-match run without a win by beating Fiorentina 3-0 on Friday. Villas-Boas, attempting to sound optimistic that Chelsea can triumph against the Serie A side, said: "It's a different competition. Napoli come into the game after a good result – not after a good run because they've been inconsistent recently – but they won well at Fiorentina.

"It's a different type of preparation, different type of football – European football, played in a different way. We will have to be much more competent, play well and try to take the game back to Stamford Bridge."

Abramovich is still to claim a first European Cup he is said to crave. "If you go past Napoli then you can have a really good chance, depending on who you get in the draw," Villas-Boas said. "First Napoli, then we will see who we draw out and then we will see. It will be a massive challenge. Everyone saw what Napoli did in a group which put another English team [Manchester City] out. But I think we will have a chance to prove ourselves."

Last week began with a mini-mutiny from players after Villas-Boas called them in the day after Saturday's 2-0 defeat at Everton, and it ended with this dispiriting draw. How will the disaffected players lift them themselves for the hothouse of Stadio San Paolo?

"Regarding the Champions League, the players will have a different outlook. It's a European game, all of the players will want to play," Villas-Boas said. "The Champions League is a competition that everyone wants to win. The players will feel much more tension. There are three weeks between the [two] games and it's important for us to be competent and to bring the game to Stamford Bridge with a win or a draw, ideally a scoring draw. Then we can finish the business here."

Of the threat of Cavani, who has 41 goals in 57 league appearances and 10 in 36 games for Uruguay, Villas-Boas said: "He is an amazing player. To be fair, their strength is in the collective spirit. They have an inner belief in each other. They have a strong front three with [Marek] Hamsik, Cavani and [Ezequiel] Lavezzi. They are a danger. We just have to be extremely strong to go through."

Villas-Boas rates Terry as "doubtful" due to a knee injury and would not be drawn on whether he will risk the captain. "The team is more important than any individual. What we are trying to do with John is to respect his importance for the team. We will try to give him a late fitness test to give him every chance."

With Torres almost certain to be dropped for Drogba, Villa-Boas hinted that Lampard will be the third senior player to miss out. "Fresh legs will be important. But the team is still to be decided," he said. "The team was a little bit tired towards the end [against Birmingham]. There's little time between the games. That will be a consideration plus the quality of the players, which is immense."

Man of the match Colin Doyle (Birmingham City)